1. Field of the Invention
The present invention relates to papermakers fabrics. More particularly, the present invention relates to forming fabrics which are used to facilitate the initial formation of a paper web during the manufacture of paper. Most particularly, the present invention provides a double layer forming fabric having an upper paper carrying/forming layer which has three or more times as many cross machine direction yarns as the lower, machine side layer.
2. Description of the Prior Art
Papermaking machines transform an aqueous slurry of fibers into a continuous paper web which can be processed for a variety of end uses. Papermakers fabrics are employed throughout the papermaking process to transport the web of paper as a continuous sheet through the papermaking equipment. The papermakers fabrics also act as a drive belt for the equipment.
The paper making process starts in the forming section of a papermaking machine where the aqueous slurry is deposited onto a forming fabric having the desired characteristics for retaining the fibers while allowing the water to pass through. The wet paper web created by this process is then carried by a press fabric through the press section where additional water is removed by squeezing the paper web and fabric between two rolls. The paper web is then carried through the drying section on a dryer fabric to remove additional water through forced evaporation. The design of papermakers fabrics used on each section of a papermaking machine vary in accordance with function.
In the forming section of papermaking machines, the fibers are retained and collected on the upper surface of a forming fabric and formed into a paper sheet. The forming fabric must have a fine mesh weave on the paper contact side in order to avoid marking the paper and to support the fiber from the slurry. The fabric must also have good drainage characteristics for initial water removal to facilitate paper formation. However, as previously noted, the forming fabric also serves as a drive belt and is subjected to high tensile loads in the machine direction and compressive or buckling loads in the cross machine direction. Therefore, a single fine-mesh yarn system is not suitable for use as a forming fabric.
To combat the prior art problem, multi-layer forming fabrics were developed with fine-mesh yarns on the paper forming surface to facilitate paper formation, and larger yarns on the machine contact side to provide strength and longevity.
Multi-layer forming fabrics are known in the art. For example: U.S. Pat. No. 4,709,732 discloses a dual layer forming fabric for use in the papermaking process; U.S. Pat. No. 5,025,839 also discloses a two-ply forming fabric with zig-zagging MD yarns; and U.S. Pat. No. 4,605,585 teaches a two ply forming fabric with a two-shaft, twill or satin weave pattern.
While these fabrics perform satisfactorily in many applications, it is desirable to provide a forming fabric having a higher degree of fiber support on the paper forming side while still maintaining good drainage characteristics.